Spectacle-glass.



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UNiTEn 4STATES PATENT ormoni if sPEo'rAoL-E-crnass.l

To all whom 'it may concern: l

for aphacic eyesbut also magnifying metrical inform.

.r the eye, strand.

. character.

--ner that correcting spectacle glasses free glasses, 'that isto Say, such collective glasses, which are designed to enable emmetropes, which are already presbyopes, to obtain distinct vision at close range.

It is well known, that a correcting glass in the form of a meniscus, when its concave surface is turned toward the eye, presents from objects lying in the peripheral parts of the field of view a somewhat less defective image than a glass more or less sym,-

rlhis fact is also true as regards magnifying spectacles. Its explanation lies in that the pencils, which Vtravel obliquely to the axis of the spectacle glass and produce in direct vision the image of the said peripheral objects, undergo, in refraction through :the likewise peripheral part of the spectacle glass, a smaller total error, when the glass is meniscal than when it is'more or less symmetrical. Moreover, it has been postulated, thata single one. of the lerrors of oblique pen'cils should be eliminated as completely as possible by suitably choosin the median curvature of the meniscus. ince the oblique |pencils, which have only a small aperture corresponding to the pupil of the eye, cross in the center of rotation of the eye, this point, which lies about 3 cm. behind the vertex of the 'concave surface, need only be regarded as the center of a narrow diaphragm, after a well known law of the dio tris of articularly emphasized y Gull y this -law the new problem of practical optics is reduced to one of known It is somewhat after this manfrom astigmatism have been calculated, for instance, by Ostwalt. p

According to patent specification 697,959,

Specification of Letters Patent. Applicationl med June 3,1909. serial No. 499,991.

l the reduction of the errors ofoblique pencils zEIss, 0E

Patched Feb. 15, 1910.

in dioptric systems having the'diaphragmj i a larger or smaller distance away from one of the spherical surfaces havin tance from' the diaphragm, suxihdeformation, in the technical sense of the word,-

consisting in varying the curvature eontinuously from the vertex to the margin, while rg retaining the property of the sur ace to be or several surfaces ofthe system, may bc" f accomplished by deforming one or several o' some disto the specification citedof sysone hand by applying the means of cor- 'i i rection according to patent specification 697,959 to the case of a spectacle glass as a 7 single lens with a small hinder diaphragm, the dist-ance of which is invariable and in addition thereto, extraordinarily large, on the other hand, however, lthrough combining this mea-nsl with the previously practiced 8 alteration of the median curvature of the meniscus.

The object of the invention is the correction, no longer of one single error of oblique pencils, but of two. of correction stated acts on the one as well as on the other of the two errors, which are intended to be corrected. Gorrection for two errors'is found .to be even feasible, when a single surface only is deformed, provided 9 that this is done not in the saine measure, but

Each of the two means in the same sense, asif the problem were to A remove, 1n a pencll the rays of which are v ration by a so-called a-planatic surface, l which, as is well known, deviates from the spherical surface corresponding to its vertex in such a manner, that its curvature from the vertex to the margin approaches continuously to the degree of curvature of the second surface, which is left spherical. Such deformation makes a dispersive spectacle glass thinner, a collective one thicker at the 1 margin..4 Since, however, in the second case 1 the practically requisite small thickness of parallel to the axis and the diameter of which is that of the lens, the spherical' aber- 95 the margin need notbe overstepped, butl from the very first a correspondingly smaller thielrnessat the vertex can be proceeded from, a reduction in the weight of the spectacle glass is in the first ease directly, in the second case indirectly, consequent upon the deformation.

The most favorable median curvature deviatcs considerably from', those median curvatures, which afford, in a spectacle glass having the same number of dioptries and belonging to the same type (according to the differentiation in the first sentence of this specification) but being in no surface deformed, the best correction of one or the other` of the same two errors of oblique pencils. All. variations of the most favorable median curvature, according to the type of' the spectacle glass and to its number of diogtries, are so limited, that neither the vertex radius of the deformed surface nor the radins of the spherical surface is shorter tlrL i of thefocal length of the spectacle "s and one at most of the two radii ex,- of the said length. lVhen astigmam and distortion are chosen as the two errors `to be removed as much as possible, an exhaustive investigation shows, that the more perfect correction is to be obtained, when the weaker curved surface is deformed.

In the annexed drawing: Figure 1 is a diagram of a' dispersive spectacle glass correcting a myopie eye for distance, this glass being corrected according to the invention. Fi 2 is a diagram of a collective spectacleY glass correcting a strongly hypermetropic or an aphacic eye for reading, this glass being corrected according to the. invention.

The dispersive meniscus according to Fig. 1 consists of` glass of Lne refractive index 1.52. It has 100 mm. focal lengt-h, its power is therefore 10 dioptries. Besides the assumption of great distance of the objects, there has been supposed a narrow hinder diaphragm D, the distance Z of which from the vertex of the hinder surface amounts to Si) mm. The radius r of the hinder surface '2.5.8 mm. The thickness ci at the vertex The front surface 'is weakly def its vertex radius 71bcing at the 5 me time the radius of the spherical surwhich corresponds to the vertex, and, having no reality, is drawn only in dots, amounts to 28.0 mm. From this spherical surface the margin of the deformed surface, having 32 mm. diameter, is only mm. dis! tant. To what. degree correction for astigmatism and distortion attained, can be seen from the follo.ving table. It contains for several obliquities w ofthe entering penfirstly, with regard to astigmatic coro the. interseetional distances s. of .igirtal and at of the meridional component of the emerging pencil, that is to y given 1n percentag say, the distances from the place of exit to the places of intersection, and secondly, with regard to the correction for distortion, which Without the employmentof deformation is strongly barrel-shaped, the so-called ratio of magnification V, in this ease the ratio between the angular distance of the object point and the linear' distance of the image point from the optical axis,

ss 99.26 min. 100.29 mm. 101.82 mm. st 99.26 97.88 102.73 V 100 99.01 98.31

The collective meniscus according to Fig.

42 is made from glass of the refractive index 1.655. Its focal length amounts to 72.59 mm., its power is consequently 13.8 dieptries. It is supposed, that the object lies in a plane which stands at right Aangles to the axis and is 380 mm. distant from the vertex of the front surface, and that a narroW diaphragm D lies at a distance 2:80 mm. behind the vertex of the hinder surface. The radius r of the front surface is 21.30 mm. The thickness at the vertex is 5.0 mm. The hinder surface is deformed. The radius ro of the spherical surface corresponding to the vertex of the hinder surface is 35.0 mm. The margin of the deformed surface, having a diameter of 34 mm., lies at a distance of i mm. from the said imaginary spherical surface. The following table contains the dimensions'explained in the first example. V, however, here means-the ratio between two lengths and can therefore be Distortion would without the employment of deformation be cushion-shaped to a very high degree.

w .0e 100.595 leales ss 86.66 mm. 88.27 mm. 91.36 mm. St 86.66 87.19 93.78 V 100% 100.57% 100.56%

l claim:

1. A spectacle glass forming a meniscus and having two errors of oblique pencil-s corrected for a small diaphragm located behind it at the distance of about 3 cm., one of the two rcfracting surfaces being deformed, so that its curvature from `the Vertex to the margin continuously approaches the degree of curvature of the other surface, neither the vertex radius of the deformed surface nor the radius of the spherical surface being shorter than g of the focal length of the spectacle glass and one at most of the two radii exceeding 31 of the said length.

2. A spectacle glass forming a meniscus and having astigmatism as well as distortion corrected for a small diaphragm located behind it at the distance of about 3` em., that of the two refracting surfaces, i

, 949,5@1 a ix which has the weaker curvature being deof the spectacle glaes and one at most of l) formed, so that its curvature from the Verthe two radu exceedlng of the sald length.-

tex to the nmrgn continuously appzoaches f the degree of cmjvature of the other surface, MORITZ VON ROHR l 5 nelther the vertex rndlus o the deformed VVltnesses: l [J surface no1' the 'mdns of the sphemcal sur- PAUL KRGER,

gl; face belng shorter than g of the 'focal lengt- FRITZ LANDER. 

